Fuse head and composition for use therefor



13, 194 1., iNGRAM 2241A FUSE HEAD AND COMPOSITION FOR USE THEREFOR Filed April 16, 1940 l 01! [(672126 YlllZ R ATTORNEY Patented May 13, 1941 UNITED s'r'ras FUSE HEAD AND COMPOSITION FOR USE THEREFOR Application April 16, 1940, Serial No. 329,868 In Great Britain May 8, 1939 14 Claims.

My invention relates to fuse heads suitable for use in the manufacture of electrically fired blasting detonators and electric fuses and for similar purposes.

The invention may be employed for exam- Die in the manufacture of low tension fuse heads. In this kind of fuse head a fine resistance wire bridging the distance between the insulated pole pieces is embedded in a coherent bead formed around it from a composition containing a heat sensitive ignitable compound and a binding agent, the ignition of the composition being brought about by the passage through the bridge wire of a low voltage electric current. The current may be a. continuous current applied by means of a battery or a pulse of short duration generated by an exploder.

My invention is also applicable to the manufacture of high tension fuse heads. In this kind of fuse head there is no bridge wi-re, but the coherent bead of heat sensitive ignitable composition comprises, in addition to the heat sensitive ignitable compound and the binding agent, an ingredient that renders it electrically slightly conducting such as graphite or lead peroxide. The potential difierence applied between the pole pieces is considerably greater than that employed in the case of low tension fuse heads, and the operation is usually carried out by means of an exploder.

The composition from which the coherent bead is formed is applied to the extremities of the pole pieces, or in the case of low tension fuse heads, to the wire bridging them, in the form of a dope made upfrom the heat sensitive ignitable compound and a solution of the binding agent. A cellulose derivative solution in a volatile organic solvent may be used and nitrocellulose solutions are usually employed. As the purpose of a fuse head is to bring about the ignition of some composition placed in its vicinity, for instance the top charge of an ordinary electric detonator, or the delay composition of a delay action detonator or a fuse, it is desirable that the fuse head should give a hot, sensitive and somewhat lasting flash. In order to achieve this it is a common practice to build up the fuse head from more than one type of composition; for instance by forming the coherent bead with a core of a composition well adapted to be ignited by r the passage'of the electric current, and an outer coating of some other composition which is not itself necessarily suitable for direct ignition by said current, but which possesses the aforesaid flashing characteristics in high degree, for inv ignition bythe electric current in low tension or high tension fuse heads. No composition is of any use that fails to ignite under the maximum current or :the maximum potential difference, as

the case may be, that is permissible in view of V the safety regulations that exist in most countries relating to the use of electricity in mining operations. But many compositions of the requisite sensitiveness to the passage of the electric cur-- rent fail because they have a tendency to disrupt with-out flame, while others again lose their capacity for ignition by the electric cur-rent on storage, especially under bad climatic conditions.

It is an object of the invention to provide new or improved fuse head bead compositions. It is also an object of the invention to devise new methods, of manufacturing low tension and high tension fuse heads. Further objects of the invention are to provide low tension fuse heads and high tension fuse heads of desirable characteristics.

According to my invention the directly ignitable composition of the fuse head bead contains, in addition to the binding agent, an aromatic compound containing a nuclear bound iodine atom attached to at least one terminal oxygen atom, said compound having an explosion point as determined by the five second test described hereunder not exceeding 300 C. The compound may be an iodoxy compound or an iodoso compound of benzene or its derivative.

By way of illustration of one form of my invention, the attached drawing shows a vertical elevation of an electric blasting initiator containing a fuse head with a bead of a composition in accordance with my invention. This is by way of illustration only, and'is not to be regarded as limiting the scope of my invention. In the drawingl represents a detonator shell of suitable metal, 2 the base charge, and 3 the primary ignition charge of the detonator.

4 represents a bridge plug holding in spaced position leg wires 5 and 6, 9 a waterproofing composition and 10, a sulphur seal. The bridge wire 1, connecting the extremities of the leg wires 5 and 6, is surrounded by an ignition bead 8 of a composition in accordance with my invention.

The iodoxy or iodoso compound used is made up into a dope with the binder and may be applied in the conventional fashion. In some cases it is advantageous to include in the composition ingredients adapted to increase the desirable characteristics of the flash, for instance metal powders such as zirconium powder, potassium chlorate, charcoal mixtures or basic lead salts of certain poly nitro phenolic compounds, for instance a basic lead 3:5-dinitro-2-hydroxy toluene or basic lead trinitro-meta-cresylate. Alternatively or in addition in forming the bead an outer coating of desirable flash characteristics made up for instance from a composition containing potassium chlorate and charcoal, smokeless powder, or a metal powder, or the like may be applied over the core of the directly ignitable composition.

Amongst iodoxy compounds which may be employed according to our invention may be mentionedz-Iodoxybenzene; ortho-meta and paraiodoxy toluene; ortho-metaand para-iodoxy chlorobenzene; orthoand para-iodoxy bromobenzene; ortho, metaand para-iodoxy nitrobenzene; para-iodoxy iodo-benzene; para-iodoxy azido benzene and iodoxy m-xylene. the iodoso compounds there may be mentioned ortho-iodoso toluene; ortho-, meta-, and paraiodoso nitrobenzene; beta-iodoso naphthalene; metaand paraiodoso azidobenzene, meta-iodoso iodobenzene and ortho-iodoso-para-nitrotoluene.

For low tension fuse heads the preferred compounds are para-iodoxytoluene, meta-iodoso-azidobenzene, para-iodoxy-azidobenzene and metaiodoso-iodobenzene; and for high tension fuse heads para-iodoso-azidobenzene, para-iodoxyazidobenzene and meta-iodoso-iodobenzene are the preferred compounds.

For the determination of the explosion point, an apparatus is employed comprising:

1. A cylindrical iron bath supported in a tripod, fitted with a sunk lid and stirring arrangement. The lid has three holes of 7 millimetres diameter to take the sample, thermometer, and stirrer.

2. A bath thermometer of a suitable range graduated in degrees.

3. A supply of No. 6 copper detonator tubes and screw collars.

4. Two auxiliary thermometers graduated from 7 room temperature to 100 C.

5. A branched glass thermometer enclosure tube.

The bathi fitted with a low melting alloy for substances requiring a temperature up to 250, and for higher temperatures solder is used. The surface of the alloy almost touches the lid. The middle of the bulb of the thermometer is placed at the same level as the bottom of the copper tube.

0.005 gm. of the substance is placed in a No. 6 copper tube and a collar screwed on at the open end of the tube. The top of the tube is flush with the top of the collar, which prevents the tube fromslipping into the bath. The bath is raised to a suitable temperature and the copper tube with sample dropped into one of the holes. The time and temperature of explosion are noted, and the temperature is altered until the substance explodes in seconds. Fresh tubes and samples are used for each alteration of temperature. Should the substance not explode the tube is held in a Bunsen flame to destroy it.

The glass tube in which the thermometer is enclosed is fitted with two branches, each of Amongst above the bath. With the aid of the auxiliary thermometers, the usual emergent stem correction is applied to the reading on the bath thermometer.

The following examples illustrate the invention.

Example 1 The following dipping composition is prepared:

Para-iodoso-azido benzene grams 2 2 /2% nitrocellulose solution in commercial amyl acetate ml 0.7

Commercial amyl acetate ml 1.9

Fuse head assemblies of the type consisting of a pressboard stamping with metal pole pieces cemented to each face and resistance wire, soldered across the ends of the pole pieces to form bridges 1 mm. long of 0.9 to 1.6 ohms resistance, are dipped in the usual way into this composition. A second dip is'given consisting of 5 parts of potassium chlorate to 1 part of charcoal, made up to dipping consistency with .a 2 /2% solution of nitrocellulose in amyl acetate; and finally a third waterproofing dip of 2 /2% nitrocellulose solution.

The fuse heads so produced fire when subjected to a current of 0.38-0.42 ampere for not more than 0.05 second. They can be fired with 15 ohms in serie by a Davis magneto 15X single shot low tension exploder, as approved for use in fiery mines by the British Home Office Mines Department. Fuse heads similarly manufactured and comprising lead mononitrorescorcinate as the ignition ingredient insteadof para-iodosoazidobenzene have a firing current of 0.44-0.48 ampere.

Example 2 stitution of meta-iodoiodosobenzene for the paraiodoso-azidobenzene. The completed fuse heads have a firing current of 0.30-0.32 ampere, and

which contains an auxiliary thermometer of range 0 to C. The glass enclosure tube minimises the fluctuations in the readings due to fortuitous variations of the air tem erature can be fired, with 40 ohms in series, by the approved -low tension exploder mentioned in Example Example 3 The following dipping composition is prepared: Para-iodoxytoluenefl gram 1 2 /2'% nitrocellulose solution in commercial amyl acetate ml 0.35 Commercial amyl acetate ml 1.2

Fuse head assemblies are dipped in this composition, and thereafter in second and third dips as described in Example 1.

The fuse heads so obtained have a firing current of 0.37-0.41 ampere, and can be fired, with 30 ohms in series, by the approved low-tension exploder mentioned in the preceding examples.

Example 4 This example illustrates the invention as applied to the manufacture of a high-tension fuse head. The following dip is made up:

Fuse head assemblies (without bridge wires) are dipped in this composition, and thereafter in second and third dips as described in Example 1.

of 33 volts is applied for not. more than 0.05 second by means of a Davis single shot IXA magneto high tension exploder as approved for use by the British Home Oflice Mines Department.

The explosion points of the preferred compounds by the five seconds test are respectively as follows:

Para-iodoso-azido-benzeneA C 148 Meta-iodoso-azido-benzene C 127 Para-iodoxy-azido-benzene C 167 Meta-iodo-iodoso-benzene C 131 Para-iodoxy-toluene C 236 I claim:

1. A fuse head bead comprising an aromatic compound containing a nuclear bound iodine atom attached to at least one terminal oxygen atom having an explosion point not exceeding 300 C.

2. A fuse head bead comprising an aromatic iodoso compound having an explosion point not exceeding 300 C.

3. A fuse head bead comprising an iodoso-azidobenzene.

4. A fuse head bead comprising para-iodosoazidobenzene.

5. A fuse head bead comprising an iodosoiodobenzene.

6. A fuse head bead comprising meta-iodosoiodobenzene. v

7. A fuse head bead comprising an iodoxy-aromatic compound having an explosion point below 7 8. A fuse head bead comprising an iodoxy-azidobenzene.

9. A fuse head bead comprising paraiodoxyazidobenzene.

10. A low tension fuse head in which the bead of the directly ignitable composition in which the bridge wire is embedded comprises an iodoxy aromatic compound having an explosion point not exceeding 300 C.

11. A high tension fuse head in which the bead of the directly ignitable composition bridging the pole piece extremities comprises an aromatic compound containing a nuclear bound iodine atom attached to at least one terminal oxygen atom having an explosion point not exceeding 300 C. and an ingredient adapted to render it conducting.

12. A high tension fuse head as claimed in claim 11 in which the aromatic compound is meta-iodoso-iodobenzene.

13. A fuse head in which the bead of the directly ignitable composition com rises an iodoxy toluene.

14. An ignition charge for electric blasting initiators and the like comprising an aromatic compound containing a nuclear bound iodine atom attached to at least one terminal oxygen atom having an explosion point not exceeding 300 C.

LOUIS KENNETH INGRAM. 

